Due to the advantages of long lifetime, small size, low heat emission, and low power consumption, LEDs have been widely applied in various home appliances and instruments as indicators or light sources. With recent development towards multicolor and high illumination, the applications of the LEDs are extended to large-sized outdoor billboards, traffic lights, etc. In the future, the LEDs may become the power-saving and environment-protecting light sources in replacement of tungsten filament lamps and mercury vapor lamps. LED chips are mainly made of compounds of groups III-V, for example, gallium phosphide (GaP), gallium arsenide (GaAs) or other semiconductor compounds. In order to enhance optical performance and reliability of LEDs, various package technologies for encapsulating LED chips are proposed.